Many types of turf maintenance equipment are known. One very common type, and the one to which the present invention most directly applies, is turf mowing equipment. Such equipment can generally be classified into those mowers which include a rotary cutting unit(s) and those which include a reel cutting unit(s). A rotary cutting unit usually includes one or more rigid, generally straight, steel blades rotated within a housing about a vertical axis to sever grass or other vegetation at a predetermined height above the ground. A reel cutting unit, on the other hand, typically includes a frame within which is horizontally rotatably mounted a reel possessing a plurality of arcuate blades. The rotating reel blades pass in close proximity to a bedknife which spans the cutting unit frame parallel to the horizontal reel axis. Grass blades are sheared at the reel blade/bedknife interface.
While rotary cutting units are suitable for many purposes, it is generally perceived that reel units provide a higher quality cut. The present invention relates primarily to turf reel mowers, and the remainder of this discussion will focus on same. As is well known, another reel-like unit is used to produce a "verticut," and this type of cutting unit is also contemplated.
Power turf mowing equipment can also be categorized based on the method of propelling the cutting units. Generally, there are walk-behind, riding, and towed turf mowers. The present invention relates primarily though not exclusively to riding turf mowers, and for the sake of brevity the invention will hereafter be discussed in terms of commercial riding mowers having one or more reel cutting units.
Riding reel-type turf mowers typically include a traction vehicle supported by a plurality of wheels, including one or more traction wheels; a prime mover supported by the vehicle frame and connected through a transmission to the traction wheel(s); and one or more reel-type cutting units, powered by the prime mover through belts or hydraulic motors, mounted to the traction vehicle in some fashion. The present invention relates in particular to the technique by which the reel units are mounted to the traction vehicle.
The cutting unit connection technique is critically important and depends on the intended applications and capabilities of the mower. Riding reel-type mowers intended for use on golf courses, for example, typically employ a cutting unit connection technique that provides two basic positions for the cutting unit(s): a lowered "operating position" and a raised "transport position". The cutting units engage the turf and mow in their operating position, whereas the cutting units are out of engagement with the turf and are not mowing in their transport position. A transport position allows the operator to temporarily raise one or more of the cutting units to mow a narrower swath or to pass through a gate or between trees. Also, it is occasionally necessary to drive the mowing machines over conventional road surfaces, at which time it is important to raise the cutting units to a transport position since they are typically not designed for repeatedly running up and down over curbs, nor for travel over paved streets. But probably the most pressing reason for a transport position is so that the vehicle can move relatively rapidly from one particular work area to another at a given site. For example, someone mowing the fairways of a golf course would have to rapidly move from one fairway to another, with the cutting units in their transport positions. Once the unmowed fairway is reached, the operator typically lowers the cutting units from their transport positions to their operating positions on the fly, i.e. with the traction vehicle moving forward. Preferably the turf is not gouged or in any way damaged when this "on the fly" transition occurs. Prior art cutting unit connection techniques often caused the reel units, as they were being lowered to their operating positions, to contact the ground in a tilted or skewed state (as shown in FIG. 4A, for example), thus gouging or at least scuffing the turf. Such a result is highly undesirable, especially on a golf course where the condition of the turf is of the utmost importance.
Riding reel-type mowers typically include so-called "lift arms" which support the cutting units in both positions ("operating" and "transport") and which raise and lower the reel units from one position to another. A lift arm is interposed between the traction vehicle and each cutting unit, and is typically an elongate (though not necessarily straight) element having a first end pivotally connected to the traction vehicle and a second end coupled to the cutting unit by means of some sort of joint, hereinafter termed an "operating unit joint" or a "cutting unit joint." The lift arm/traction vehicle joint, at the first end of the lift arm, is typically though not necessarily a simple pivot joint permitting only one "degree of freedom" relative to the traction vehicle, and this joint is hereinafter termed a "lift arm joint." The pivot is typically about a substantially horizontal axis. The cutting unit joint between the lift arm and the cutting unit is oftentimes more involved, depending on the objectives being sought. The present invention is particularly directed to an improved cutting unit joint for a reel-type mower of the type generally described above.
One important capability of reel-type riding mowers, particularly those for use on golf courses, is to be able to cut the turf with great precision. That is, the height of cut must be extremely consistent across the entire width of the mower, regardless of the terrain. This requires that the cutting unit(s) "float" relative to the traction vehicle. A truly free-floating reel unit can follow the contours or undulations of the ground irrespective of the relatively gross motion of the traction vehicle. If reel units are not supported in a floating manner, they tend to scalp the higher regions and skip over the lower regions.
The lift arm joint typically allows for one "degree of freedom" of the cutting unit: if the cutting unit needs to move up or down, relative to the traction vehicle, to follow turf undulations, the lift arm pivots on the traction vehicle to permit this to happen. But it is the cutting unit joint, the joint between the lift arm and the cutting unit, that is usually called upon to provide most of the flexibility needed to accommodate a more or less free-floating cutting unit. That is, the cutting unit joint typically provides for the other degrees of freedom often associated with a high precision floating cutting unit of the type used on golf courses and similarly demanding locations. These other degrees of freedom can include "rolling" (pivoting side to side about a longitudinal axis); "yawing" (pivoting about a vertical axis); and "pitching" (pivoting about a lateral axis), to make use of aviation terms to describe various motions of a reel-type cutting unit as it follows the turf.
One commonly desired characteristic of a cutting unit joint is to permit limited "steering" of the associated cutting unit, steering being but one type of "floating" as discussed above. A cutting unit is said to "steer" when it yaws (to again borrow an aviation term) about a vertical axis formed by the cutting unit joint so as to minimize skidding of the cutting unit as the mower traverses a turn. This steering action is typically achieved by making the cutting unit joint in the general nature of a caster wheel joint, so that steering or castering occurs automatically during a turn without having to actively force the cutting unit to yaw with a force producing element such as a hydraulic cylinder.
If the cutting units are not permitted to steer, then the rollers supporting the cutting unit will tend to slide laterally, i.e. skid, to some degree when the mower negotiates a turn. If a so-called Wiehle roller, one which includes a plurality of circumferential grooves along its entire length, is used in conjunction with a non-steering cutting unit, then skidding and turf scuffing is even more likely. And a cutting unit which is sliding laterally even slightly does not provide as clean a cut as a cutting unit which is accurately tracking the turn, i.e. aligned such that an axis passing through the cutting reel is perpendicular to the direction of travel of the traction vehicle at any given instant in time.
Thus for many mower applications it is advantageous to have a cutting unit joint, between the lift arm and the cutting unit, which provides limited steering. But a steering cutting unit joint can create problems as well. For example, a steering cutting unit joint can make the cutting unit overly "floppy" when it is in its raised transport position. This can create unnecessary noise (and wear) as the cutting unit bangs against mechanical "stops" which establish maximum angular limits to the steering or yaw. This banging might even cause the cutting unit to lose its height of cut adjustment over a period of time, a significant problem especially for users who do not check their height of cut setting on a regular basis. And a steering cutting unit joint can also contribute to the phenomenon depicted in FIG. 4A. This drawing shows a front elevational view of a cutting unit which is tipped to one side which, if lowered to the turf "on the fly," would cause damage to the turf. The lowermost corner of the cutting unit would be the first thing to engage the turf, and this corner would dig into the turf. A steering cutting unit joint can contribute to this phenomenon in the following way: especially in the context of a cutting unit joint which permits side-to-side tipping, or "rolling" (again borrowing an aviation term), of the cutting unit, a steering-type cutting unit which is yawed completely over against one of the stops can become imbalanced and then tip or "roll" to the position shown in FIG. 4A. Once the cutting unit is in this tipped state, lowering the cutting unit "on the fly" (from the transport position to the operating position) can definitely cause damage to the turf.
The present invention addresses the problems possessed by prior art cutting unit joints. In particular, the present invention includes a cutting unit joint which can accommodate controlled steering and even "rolling" in a preferred embodiment, but which also decreases the likelihood of a tipped cutting unit (as shown in FIG. 4A) and thereby reduces turf damage. A preferred cutting unit joint according to the present invention can permit "floating" of the reel unit; accommodate existing reel unit lifting techniques; and reduce turf damage during "on the fly" transport-to-operating position transitions.